Stable chromium-nickel-iron alloy



LMS

Maw' Mr, w35 v. B. BROWNE l STABLE CHROMIUM-NICKEL-IRON ALLOY Filedsept. 2, 1935 HMH INVEN'oR @am @7mm Patented May 14, 1935 UNITED STATES 2,001,123 STABLE CHBGMIUM-NICKEL-IRON ALLOY Vere B. Browne, Brackenridge, Pa., assigner to Allegheny Steel Company, Brackem'dge, Pa.,

a corporation of Pennsylvania vApplication'September 22, 1933, Serial No. 690,537

Claims.

, This invention relates to austenitic chromium nickel iron alloys or steels of the type known generally as 18-8and this application is a continuation in part of an application filed by me on Feb.

5 11, 1930, Serial No. 427,652 for Stable chromium nickel-iron alloys.

While alloys or steels containing about 18% chromium and about 8% nickelmay be termed the standard 18-8 alloy, the` 18-8 type embraces a chromium range of from about to about 30% and a nickel range of from about 5% to about Alloys of this type have a wide range of usefulness and are of particular value in the chemical and allied industries if they are not susceptible to intercrystalline disintegration and subsequent deterioration after being welded.

Welding of alloys of this type necessitates local heating to temperatures of from 800-1500 F. for short periods of time and it has been found that many alloys of the 18-8 type when subjected to short time heating within this temperature range exhibit a marked tendency toward intercrystalline deterioration. The change which results from such heating appears to consist in a separation of one or more elements from `the grains or crystals; the alloys also' ecome slightly magnetic. Upon heating within the range of 800-1500 F.,

with some alloys of this type the carbon separates as a carbide between the grain boundaries. The

` addition of other elements may have an eiiect on this phenomenon. One result of such a change in y'the structure of the carbon containing alloys of ythis type is that the carbide, or other newcomponent or components which form between the grain boundaries, is frequently,electro-positive to .the crystals, and when the alloy is subjected to corroding influences, local electrolytic action sets up between the separated carbide or other components, and the crystal itself, invariably resulting in a rapid corrosion and disintegration of the y alloy. When some alloys of ythis type are heated within vthe above temperature range, the resulting structural change is so pronounced that when subjected to a corroding solution the grains actually fall apart, and deposit in the form of a powder in 'av corroding solution which will not aiect the alloy prior to suchheating.

A. In connection withialloys or steels'of this type y vhavinga chromium range of from lll-25% and a nickel range offflrorn 'l-12`%,-it has been proposed to'fkeep thehcarbon(content'below .07% ih order to secure immunity, tofrintercrystalline deteriora- `tionzwhen subie t d toheating withinthe equivalent toa tempering temperature (see British Patent No. 305,654, dated Jan. 14, 1929 v It is diiiicult and expensive, however, vto make such extremely low carbon alloys due to the price of low carbon alloying elements. Furthermore, such low carbon alloys have certain undersirabl'e properties such as low elastic limit and low resistance to reverse bending stresses. An alloy 'containing approximately twenty six percent of chromium and nickel combined in the proportion of about 18% of chromium and about 8% of nickel, will be relatively stable provided the carbon content is less than .07%. Such an alloy may be called a standard alloy or steel for purposes of this application. By decreasing the total content of chromium and nickel, or by increasing the carbon content of such an alloy or steel, stability is lost.

During the course of extensive research dn alloys of this type, and especially with alloys containing about twenty-six percent of chromium and nickel combined, in the proportions of about 4eighteen percent of chromium, and about eight percent of nickel, with the balance principally iron, I have found that alloys can be made which 25,

are more sluggish and reluctant to dissociate when heated within the range of decomposition (800-1500 F.) by carefully regulating the total content of chromium and nickel in relation to the carbon content. These alloys need not be 30 annealed after being subjected to a short time heating within the range of decomposition, as in welding, to avoid subsequent intercrystallne corrosion in service.

An object of this invention is to produce austenitic chromium nickel alloys or steels having a carbon content of from .G7-.20% which are characterized by denite sluggishness or reluctance to dissociate and which do not subsequently develop intercrystalline deterioration.

Another object of this invention is to produce chromium-nickel steels which have a carbon range of from .G7-,20%, a chromium range of from about 15% to about 30%, `and nickel range of from about 6% to about 16% with a combined chromium nickel range of from about 26% to about 40%, an'd which are characterized by practical immunity (because of the abovestated denite and substantial sluggishness) to intercrystalline disintegration and subsequent deteriora- 0 tion when subjected to normally.: corrosive media after heating as in welding withinI a temperature range of from 8001500 F. 'andwithout being subsequently annealed at a'higher temperature.

'A further object of this vinvention is to produce an article of manufacture characterized by immunity to intercrystalline and intergranular disintegration and subsequent deterioration when subjected to normally corrosive media after heating within a temperature range of 80G-1500" F. for a short time without being subsequently annealed at a higher temperature and made from a chromium nickel steel having a carbon content of from .C7-.20%, a chromium range of from about 15% to about 30% and a nickel range of from about 6% to about 16% with a combined chromium nickel range of from about 26% to about 40%. l

A still further object of this invention is to produce a welded article of manufacture which, without having been annealed, is characterized by immunity to intercrystalline disintegration and subsequent deterioration when subjected to normally corrosive media and which isfabricated from a chromium nickel steel having a carbon content of from .07.2%, a chromium range of from about 15% to about 30% and a nickel range of from about 6% to about 16% with a combined chromium nickel range of from about 26% to about 40%.

During the research above noted I found that with many alloys of this type, when the chromium, or nickel, or both have been increased so that the total exceeds twenty-six per cent, the alloys exhibit a resistance to corrosion in excess of that obtained with what has been termed the standard alloy. Upon subjecting these new alloys to accelerated tests, using a definite corroding medium, such for example, as a solution of sulphuric acid saturated with copper sulphate, I found that those alloys with high chromium and nickel content have exhibited phenomenal resistance to corrosion. I also found that others having lower percentages of combined chromium and nickel and the same carbon content disintegrated in a short time.

The following table illustrates the influence of the relation between the three elements, chromium, nickel and carbon, when subjected to an accelerated test in a corroding solution after being heated to about 1200" F. for one hour:-

It will be noted that the combined chromium and nickel in alloy (2) equals about twenty-three percent, with 0.06 carbon, and had a life of 46 hours in the corroding solution; while that of alloy (l) corresponding to the standard alloy, with about 26 percent of chromium and nickel and about the same carbon, had a life of 384 hours. Also that alloy (6) with 26.8 percent of combined chromium and nickel, and with 0.20

percent carbon, had a life of but one-half hour,

while alloy with about 34 percent of combined chromium and nickel, and with 0.20 percent carbon, had a life of 76 hours in the corroding solution.

With all of the alloys of the austenitic type, I have found that by adjusting or proportioning the total content of the chromium and nickel to years.

the increasing carbon content, as described herein, the resistance to the disintegratng influence of short time heating with the range of dissociation (800-1500 F.) is substantially increased when compared with an 18 percent chromiumand 8% nickel alloy of the same carbon content. Whenthe percentage of chromium and nickel combined is increased above twenty-six percent, in the general proportions of nickel equaling about one-half of the chromium, the carbon content may be safely increased above that of the standard alloy referred to herein. For example, with combined chromium and nickel suflciently high, the carbon may be as high w .20%. I'hese new alloys, by virtue of their balanced composition so definitely retard decomposition that when heated for a short time as in a welding operation they are unaffected by subsequent service of various types under which the standard alloy of 18% chromium and 8% nickel with the same carbon content would be seriously affected. Such new alloys may be successfully used in the fabrication of many variedv types of metal articles 'which during use are subjected to corroding agents, such as Various chemicals, exposure to the weather, fumes, sprays, vapors, and the like, and are especially useful for the manufacture of welded articles.

In the accompanying drawing which forms a part hereof, I `have illustrated in graphic form the relationship between the total chromium and nickel content and the carbon content wherein the carbon content is plotted against the total chromium and nickel content for each composition shown. The experimental results depicted in the graph were obtained by subjecting the samples to the corrosive action of sulphuric copper-sulphate reagent (boiling for 50 hours), the said samples being first subjected to heating at 1200 F. for 20 minutes, this time being very much longer than that encountered in welding.

Referring to the drawing, it will be understood that the graph illustrates only that portion of the total chromium plus nickel content which lies between about 26 and 28%. The carbon content for this chromium plus nickel range increases from .07% to .15% and I have discovered that regardless of the exact range the relationship may be expressed in terms of a formula which determines the minimum of chromium and nickel content for what I term a balanced composition and which is accordingly a convenient manner of defining lpart of my present invention. 'I'his formula consists of an equation which may be written as follows:-

Chromium plus nickel equals 26% plus 22 (carbon minus .06).

For example, in a'welding operation a portion of the alloy is within the stated dissociation range only for a short time and the graph indicates the minimum balanced chromium-nickel carbon composition which renders the alloy immune from decomposition, without subsequent annealing, when subjected to certain conditions of service.

' For the sake of providing comparisons and showing what may or may not be expected from the present invention, I have in addition plotted, on the same graph, results on sheets of different compositions which were taken from a pasteurizer which had been in service for more than two This pasteurizer was made up by welding together commercial sheets of 18-8. It is noteworthy that some of these sheets failed adjacent the welds and others were perfectly -satisfactory after two years service depending upon the composition of the sheets and these results likewise appear on the graph for comparative purposes. In general, it may be saidthat those welded sheets which had compositions lying above the line AB proved to be satisfactory, whereas those compositions falling below the line AB failed by disintegration.

For other kinds of service Where particularly heavy sections are involved and where it is necessary to weld such sections or otherwise subject them for short time periods to a temperature within the range of from about 800 F. t0 about 1500 F. I nd it advisable to use higher than the predetermined minimum for combined chromium and nickel content.

The presence in the alloys of such elements as silicon, tungsten, molybdenum, copper, or vanadium, singly or collectively, in quantities varying from a trace up to about three percent, will merely shift the line downward.

What I claim as new and desire to secure by Letters Patent is:

1. An article of manufacture for use in the chemical, metallurgical and physical fields characterized by substantial immunity to intercrystalline and intergranular disintegration and deterioration by being capable of being raised to temperatures of 800 to 1500 F. as to-any portion thereof for welding purposes without subsequent annealing at higher'temperature and without loss of structure or characteristics as to such portion, and containing substantially onlyV the following elements in substantially the following proportions as a stable austenitic structure, chromium from approximately 15% to approximately 30%,v

nickel from approximately 6% to approximately 16%, the proportions of nickel and chromium being such that the` total chromium and nickel contents range from approximately 26% to approximately 40%; the nickel equaling about 30-70% of the chromium content; carbon being present from .07 to approximately .20% and iron consti-- tuting substantially the entire balance except for the usual impurities in common amounts, in accordance with the line A--B of the graph as herein set forth.

2. An article of manufacture for use in the chemical, metallurgical and physical fields characterized by substantial immunity to intercrystalline and intergranular disintegration and deterioration by being capable of being raised to temperatures of 800 to 1500 F. as to any portion thereof for welding purposes without subsequent annealing at higher temperature and without loss of structure or characteristics as to such portion, and containing substantially only the followingelements in substantially the following proportions as a stable austenitic' structure; the combined percentages of chromium and nickel being about 26 to 40%, of which nickel is approximately to 40% of the total chromium and nickel contents and of which chromium is approximately 60 to 75% of the'total chromium and nickel contents; carbon being present from .07% to approximately .20%, and iron constituting substantially the entire balance except for the usual impurities in common amounts, in accordance with line A-B of the graph as herein set forth.

3. An austenitic chromium. nickel iron alloy adapted for use in manufacturing welded articles for the chemical metallurgical and physical arts, in which the total chromium and nickel contents range from approximately 26-40% with approximately Sil-70% as much nickel as chromium, the carbon content of the alloy ranging from .07% to approximately .20%, the balance ofthe alloy being substantially all iron except for the usual impurities in common amounts, said'alloy, and

hence articles fabricated therefrom, being characterized by substantial immunity to intercrystalline and intergranular disintegration and deterioration after being'subjected without subsequent annealing at higher temperature, to the dissociation range of 800-1500" F. for a short time, as

, in a welding operation, such immunity-being present when the totall chromium plus nickel content on the one hand and the carbon content von the other hand have the minimum relationship set forth by line A-B of the accompanying graph as herein set forth.

4. A welded article for usel in the chemical,

metallurgical and physical fields, which without being annealed after welding is not susceptible `to intercrystalline corrosion when in contact with corrosive media and which is made from a steel containing between 1530% chromium, 6-16% nickel and carbon from .D7-.20%, the nickel content `being from :iO-70%, of the chromium content, such steel being characterized by definite sluggishness and reluctance to dissociate when heated within the range of decomposition and in which the minimum combined chromium and nickel in relation to the carbon content is in accordance with line A-B of the graph.

5. An austenitic steel which is characterized by a definite sluggishness and resistance to dissociation when heated for a short time within the range of decomposition 80G-1500" F. as in a welding operation and which, without being annealed after such heating is not susceptible to intercrystalline corrosion when in contact withcorrosive media; said steel containing chromium from about 15% to about `3,0%, nickel from about 6% to about 16%, and carbon from .G7-20%; the nickel content being from 30% to 70% of the chromium content and the combined chromium and nickel content for any carbon content within such range from .G7-.20% being not less than that defined by the line A-B of the graph herein set forth.

VERE B. BROWNE. 

